1. Field of the Invention
The present invention relates to the improvement of an error detecting unit of a motor rotation control device, and more particular to an error detecting unit of a motor rotation control device of which error can be instantaneously detected.
2. Description of the Prior Art
Generally, a motor rotation control device is provided with a rotational detector such as an encoder attached to the motor.
The rotational detector outputs two kinds of rotation detection signals (A, B) having a phase difference (for instance 90 degrees) and the equal frequency according to the rotation of motor.
The time charts in FIG. 4 and FIG. 5 show an example of the rotation detection signals A (.phi.A) and B (.phi.B), and the time charts show the conditions of the rotation detection signals when the motor rotates counterclockwise (hereinafter called "CCW direction") and rotates clockwise (hereinafter called "CW direction"), respectively.
This motor rotation control device outputs a commanding signal for appointing the direction of rotation of the motor to make the motor rotate, and the actual direction (CCW direction or CW direction) of rotation of the motor is obtained according to difference of the level (low level or high level) of the rotation detection signal B on the upstroke of the rotation detection signal A (the time (j) and (k) in FIG. 4, the time (1/4) and (m) in FIG. 5), thereby causing the motor to be driven and controlled.
In usual driving of the motor, the rotation commanded direction of the motor is coincident with the actual direction of rotation thereof.
However, according to such a motor rotation control device as shown in the above, reverse drive force is given to the motor by changing the rotation commanded direction when changing the direction of rotation of the motor or braking the motor, thereby the motor rotation can not be reversed instantaneously from the current actual direction of rotation thereof. Therefore, when changing the direction of rotation or braking, the rotation commanded direction of the motor is compelled to be opposite to the actual direction of rotation thereof.
For example, the ensuing description copes with the case of changing the direction of rotation of the motor by utilizing the time chart in FIG. 6. In the case that the rotation commanded direction of the motor is changed to the CW direction (the time (g)) when the motor rotates in the CCW direction (the period of time (f) through (g)), reverse drive force is given to the motor and the motor is speed-decelerated (the period of time (g) through (h)). After that, the actual direction of rotation of the motor is changed from the CCW direction to the CW direction (the period of time including and after (h)).
Therefore, in the above period of time (g) through (h), the actual direction of rotation of the motor becomes opposite to the rotation commanded direction.
On the other hand, as shown with a dashed line X in FIG. 6, the period of time during which the actual direction of rotation of the motor becomes opposite to the rotation commanded direction is the period of time (g) through (i) in braking the motor as well as in the case of changing the direction of rotation.
A method for judging that the motor rotation control device is out of order when the rotation commanded direction of the motor is not coincident with the actual direction at other time than in changing the direction of rotation or braking the motor as shown in the above has been usually utilized as a conventional error detecting unit of the motor rotation control device.
A method for judging the agreement of respective directions of rotation after the appointed period of time .DELTA.T (the period of time (g) through (h)) from the time of changing the rotation commanded direction of the motor when changing the direction of rotation of the motor from the CCW direction to the CW direction as shown in FIG. 6 to the time at which the appointed direction of rotation of the motor becomes coincident with the actual direction of the motor elapses is, for instance, listed as one of the examples of the aforementioned error detecting methods.
In the conventional method, however, it is necessary to wait for judgement of the error until the actual direction of rotation of the motor coincides with the rotation commanded direction after having changed the rotation commanded direction of the motor. So, the method has a fault that any error of the motor rotation control device can not be detected in the meantime.